Beware the Fukushima Sushi

Few American consumers would mourn the loss of the anchovy. If it weren’t for pizza or Caesar salads, there might be no use for the little salty fish at all. But few people want to see the ocean’s anchovy stocks wiped out by radiation either. That’s just the scenario that seemed to be developing, however, when reports coming out of Japan revealed that elevated levels of cesium-137 had been found in anchovies in the waters off Chiba, near Toky0—a direct result of the ongoing crisis at the Fukushima Daiichi power plant.

That, however, was not nearly the most alarming news of the day. Far more troubling were reports that levels of radioactive iodine-131 were also climbing off Japan’s coasts—rising to a shocking 4,385 times the safe and legal limit. Exceeding any such threshold by a factor of 4,385 seems like an environmental apocalypse, but is it? Are the oceans beyond saving—and what about the anchovies?

The sea creatures most at risk from radioactive contamination are soft-bodied animals, such as jellyfish and marine worms, which absorb pollutants readily. Shellfish are less susceptible, as are finned and scaly fish—at least initially. The very first creatures to absorb radioactive particles are tiny zooplankton and phytoplankton, which take hold of pretty much anything they come in contact with that could pass even remotely as food. In the big-fish-eats-little-fish way of the ocean, the radioactive contamination eventually gets passed up the food chain, concentrating in fats which get consumed and stored, until the isotopes finally come to rest in the very largest creature at the top of the food chain‚ the whales, dolphins and sharks.

You’d need an enormous amount of radiation to kill fish outright and while that does happen, it’s uncommon. Rather, the isotopes damage the organisms’ genes, causing some individuals direct harm, but mostly causing genetic changes to be passed onto subsequent generations. This can destabilize the overall population if too many fish inherit an undesirable or maladaptive trait—though the strict hand of natural selection also means that when those afflicted fish die out, they can no longer pass on whatever genetic defect they’ve inherited.

How harmful contaminated fish can be to humans is an open question. The anchovies probably pose little risk, since their level of cesium contamination was measured at just 3 becquerels per kilogram. A becquerel is a unit of radioactivity in which one atomic nucleus decays every second. That’s an unhelpful definition for anyone trying to gauge what’s safe to eat, but no matter what a becquerel is, three of them aren’t much. Japanese health authorities peg the unsafe level at 500 becquerel per kg. What’s more, while anchovies tested dirty, other fish, including mackerel. spear squid and olive flounder didn’t.

The biggest worry about cesium is how long it stays around. The half life of the isotope is 30 years, and since radioactivity levels are not considered completely safe until ten to 20 times longer than the given isotope’s half life, the cesium spilled today could still be a food chain contaminant six centuries from now.

More troubling is the astronomically high iodine level. The World Health Organization (WHO) has published new guidelines that do urge consumers to “avoid consumption and harvesting of aquatic animals and plants (including fish, shellfish, and algae)” in areas “confirmed to be seriously contaminated,” which does mean lay off the Fukushima sushi—and any ocean product from any affected waters.

Two things working in consumers’—not to mention the fish’s—favor are the enormity of the ocean and the volatility of iodine. However much water the crippled nuke plant spills, it becomes quickly diluted once it flows off the coast. What’s more, the half-life of iodine-131 is only eight days, which means that after the nuke crisis ends, the ocean may need just six months to clear itself.

The big x-factor, of course, is that after-the-nuke-crisis-ends part. The Fukushima disaster began three weeks ago and there is currently every sign that it could easily be under way three weeks from now—and perhaps a good deal longer. Until then, heeding guidelines and eating carefully is the only—or at least best—option.